This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
That whole construct is called an immediate function. The function is declared, executed and discarded all in that same statement. The (jQuery) portion of the statement is the function's argument list. It's assigned to the $ parameter of the function.
It forces the $ to equate to jQuery within the function, even if something outside of the function redefines $ to mean something else.